From the Guidelines
Elevated Blood Urea Nitrogen (BUN) levels in patients with gastrointestinal bleeding occur primarily due to increased protein absorption from the digested blood in the intestines, as well as potential pre-renal azotemia from volume depletion, as supported by the most recent evidence 1. The mechanism behind this elevation involves the breakdown of blood proteins by digestive enzymes into amino acids and peptides, which are then absorbed into the portal circulation and transported to the liver for deamination, producing ammonia that is converted into urea, leading to increased urea production and consequently elevated BUN levels. Some key points to consider in the context of GI bleeding and BUN elevation include:
- The incidence and management of nonvariceal upper gastrointestinal bleeding, as outlined in recent guidelines 1
- The importance of resuscitation and maintenance of hemodynamic stability in the initial management of nonvariceal UGIB 1
- The role of esophagogastroduodenoscopy as the usual first-line diagnostic and therapeutic investigation for UGIB 1
- The potential for pre-renal azotemia due to volume depletion, which can further contribute to BUN elevation 1
- The characteristic "prerenal BUN elevation pattern" with a disproportionate rise in BUN compared to creatinine, which can serve as an indirect marker for GI bleeding, particularly upper GI bleeding 1
From the Research
Causes of Elevated BUN in GI Bleed
- Elevated Blood Urea Nitrogen (BUN) levels in patients with Gastrointestinal (GI) bleeding can be caused by several factors, including:
- Under-resuscitation, which can lead to a decrease in blood volume and a subsequent increase in BUN levels 2
- Bleeding in the upper GI tract, which can cause an increase in BUN levels due to the absorption of blood into the bloodstream 3
- Dehydration, which can concentrate the blood and increase BUN levels 4
- The BUN/creatinine ratio can be used to determine the severity of GI bleeding and bleeding localization, with a higher ratio indicating upper GI bleeding 3
Relationship Between BUN and GI Bleed
- An increase in BUN at 24 hours is a significant predictor of mortality in patients with acute nonvariceal upper GI bleeding (UGIB) 2
- Patients with an increased BUN are more likely to experience worse clinical outcomes, including inpatient death, inpatient rebleeding, and need for surgical or radiologic intervention 2
- The BUN/creatinine ratio is a sensitive and noninvasive biomarker for distinguishing between upper and lower GI bleeding, with a cut-off value of 23.3 demonstrating high sensitivity and specificity 3
Clinical Implications
- Elevated BUN levels in patients with GI bleeding should be carefully evaluated and managed to prevent under-resuscitation and worsening of clinical outcomes 2, 4
- The use of proton pump inhibitors (PPIs) and other medications may help reduce the risk of GI bleeding in certain patients 5, 6
- Early endoscopy and intervention may be necessary to prevent recurrent bleeding and improve outcomes in patients with GI bleeding 5, 4